Pancreatic ductal adenocarcinomas (PDACs) overexpress all three transforming growth factor beta (TGF-2) isoforms and inhibitory Smad7, and frequently harbor Kras mutations. High TGF-2 levels in PDAC correlate with disease progression, yet Smad7 and oncogenic Kras generally block TGF-2-mediated Smad2 and Smad3 nuclear translocation, implicating dysregulated TGF-2 signaling in PDAC. In this proposal we will test the hypothesis that Smad7 overexpression contributes to pancreatic cancer progression and metastasis by modulating TGF-2 actions in cancer cells in a manner that promotes their growth, survival and chemoresistance, and that Smad7 synergizes with mutated and constitutively active Kras to promote pancreatic cancer progression and metastasis. Three approaches will be used to test this hypothesis. First, the consequences of Smad7 overexpression in three PDAC cell lines will be determined in vitro with respect to biological actions and signaling, and in athymic mice with respect to tumor formation, growth, invasion, metastasis, angiogenesis and apoptosis. Second, mice that express transcriptionally silenced (LoxP-Stop-LoxP) Smad7 in Nestin-expressing cells will be generated for breeding with mice expressing Cre recombinase under control of the Pdx1 promoter (Pdx1-Cre), in order to assess the role of Smad7 alone in the initiation and progression of pancreatic cancer. Animals carrying both Nestin-LSL-Smad7 and LSL- KrasG12D alleles will then be bred to the Pdx1-Cre mice in order to look for in vivo synergy between Smad7 and mutated Kras. Only the triple compound mutants will have activated Kras expressed in the whole pancreas while Smad7 expression will overlap only with the Nestin-expressing subpopulation. Third, since high Smad7 levels lead to the functional inactivation of pRb, mice that express Rb with a floxed Stop cassette in the introns flanking exon 19 (LSL-Rb) will be bred with mice carrying LSL-KrasG12D alleles and Pdx1- Cre, in order to determine whether mutated Rb mimics the in vivo actions of Smad7. Pancreata from control and mutant mice in aims II and III will be analyzed histologically at defined time points, and the consequences on pancreatic intraepithelial neoplasia (PanIN), cancer formation and altered TGF-2 signaling will be determined. Project Narrative: Pancreatic ductal adenocarcinoma (PDAC) is the fourth leading cause of cancer death in adults in the United States, with mortality virtually equaling incidence. This disease may be an even more serious problem in the future since its incidence increases after age 50 and the general population in the United States is aging. This proposal aims to provide an improved understanding of the biological causes that contribute to this disease aggressiveness, with the ultimate goal of devising better diagnostic and therapeutic strategies.